Sample size justification: The primary outcome used to determine sample size for a future larger RCT is the Bayley III cognitive composite score 2 years post-operatively. The minimal clinically important difference for the Bayley III cognitive score is half a SD. This is a medium effect size usually considered to indicate different classes of patient outcome. The Boston Circulatory Arrest trial was designed to detect a difference of half a standard deviation in intelligence quotient, and considered the detected 6.5 point deficit in Psychomotor Development Index of the Bayley (43% of a SD) clinically significant. Our data from the CPTP shows a mean Bayley III cognitive score of 91 with SD 16. To detect an 8 (half a SD) point increase in the mean cognitive score at 2 years with an alpha of 0.05 and a power of 0.8, we need 63 patients per group. In the CPTP cohort studies, loss to follow up has been <2% at 2 years, and exclusion criteria were met by about 5% of eligible neonates in 2009. Loss to follow up is unlikely in these patients because they need frequent follow up visits with the pediatric cardiologist and pediatricians. To account for loss to follow up and early withdrawal from the study we plan to enroll a total of 140 patients (70 patients in each group) in the future study. The Stollery Children's Hospital is the referral center for pediatric cardiac surgery in Western Canada, all the neonates having heart surgery are transferred to the Stollery preoperatively. The enrollment of 50 patients in 1 year in the pilot study would determine that recruitment of 140 patients in 3 years is feasible. Furthermore, based on data from our center (mean peak lactate level 4.6, SD 2.4) a sample size of 50 patients will allow us to detect a 50% reduction in peak lactate level on day 1 post-operative with an alpha (two sided) of 0.05 and 0.9 power.